Just been out trial packing the cars to see what does, and doesn't fit - now that we are 3
So, what we have here is:
In the boot - Samsonite trolley case (pictured is the MINI specific one, but a standard one fits fine too) and a Bugaboo Cameleon frame (wheels off and stored on the boot floor).
With one seat down, the Cameleon carrycot fits, strapped in using the passenger seatbelt (because of the way it all wedges in, it barely moves when out and about - it survived the Hightown bends test, Mikey

).
We can fit a weekend's worth of clobber for the 3 of us between the trolley case and the carrycot. As you can see in the photo there is still oddments space in the boot for small bags, jackets etc (packed on top of the case, around the frame).
Car seat is a Maxi Cosi Cabrio on an Isofix base. The Bugaboo change bag fits conveniently behind the passenger seat.
The Bugaboo Cameleon frame fits in the boot with the seats up and one wheel removed, ideal for using with the car seat. Again, there is oddments space around the frame for a few small shopping bags. Alternatively, one could always try
Ocado
Hope this helps
